Ether promoters for lewis acid catalyzed isomerization process

ABSTRACT

ADDITION OF ETHERS AS PROMOTERS FOR LEWIS ACID CATALYZED ISOMERIZATION, PREFERABLE TAKING PLACE WITHIN A HALO-AROMATIC SOLVENT, RESULTS IN THE SUPPRESSION OF CRACKING AND A CORRESPONDING MAXIMIZATION OF THE DESIRED ISOMERIZATION PRODUCTS. THE ETHERS CONTAIN AT LEAST ONE SECONDARY OR TERTIARY ALKYL RADICALS OR CYCLOALKYL RADICALS.

United States Patent 3,641,185 ETHER PROMOTERS FOR LEWIS ACID CATALYZED ISOMERIZATION PROCESS George M. Kramer, Berkeley Heights, N.J., assignor to Esso Research and Engineering Company No Drawing. Filed June 16, 1969, Ser. No. 833,694 Int. Cl. C07c /30 US. Cl. 260-683.76 12 Claims ABSTRACT OF THE DISCLOSURE Addition of ethers as promoters for Lewis acid catalyzed isomerization, preferably taking place within a halo-aromatic solvent, results in the suppression of cracking and a corresponding maximization of the desired isomerization products. The ethers contain at least one secondary or tertiary alkyl radicals or cycloalkyl radicals.

PRIOR ART This invention relates to the use of promoters in the Lewis acid catalyzed isomerization of parafiins. More particularly, the invention relates to improvements in the liquid phase conversion of normal or branched chain hydrocarbons to the more desirable highly branched isomers. This conversion is, according to the instant invention, greatly improved by the addition of an ether to said Lewis acid system, said ether containing at least one secondary or teritary grouping.

In the past, a great deal of efiort has been expanded in various attempts to improve the isomerization reaction. Basically, it has been recognized that cracking is an undesirable side reaction associated with high catalyst consumption and must be minimized. Thus, cracking must be inhibited both to suppress the formation of unwanted hydrocarbon products and to extend the useful life of the catalyst.

The prior art contains many different techniques for inhibiting cracking in the isomerization reaction.

Generally, these techniques involve the use of naphthenes, aromatics and hydrogen as cracking suppressors; but little attention has been paid to the role of initiating reagents in influencing the selectivity of the isomerization reaction. The suppressors are used in conjunction with the traditional promoters which are required to initiate the isomerization of paraflins over Lewis acids; such promoters include trace amounts of olefins and hydrogen halides, as well as alkyl halides, water and oxygen. An extended discussion of the suppressors and promoters is to be found in H. Pines and J. M. Marity The Chemistry of Petroleum Hydrocarbons Chapter 39, Brooks, Kurtz, Boord & Schmerling, Reinhold Publication, vol. #8, 1955. The disclosure of which is herein incorporated by reference.

More recently, in US. Pat. 2,956,097 the use of a perhalogenated carbonaceous compound in which one of the halogen atoms is fluorine is recommended for use as a promoter in the isomerization reaction at critical temperatures. This type of promoter and others which have been utilized contemporaneously with it have met with limited success in facilitating the economical isomerization of paraflins since, although, they successfully promote the reaction they do not simultaneously suppress the undesired cracking.

SUMMARY OF THIS INVENTION According to this invention, it has unexpectedly been discovered that the addition of particular ethers as promoters for a Lewis acid catalyzed isomerization, preferably taking place within a halo-aromatic solvent, results in the suppression of cracking within the isomerization.

reaction and a corresponding maximization of the desired isomerization products. The ethers may be employed with or without conventional cracking inhibitors. The particular ethers to be utilized are those having at least one secondary or tertiary alkyl, secondary cycloalkyl or tertiary cycloalkyl grouping. The ethers will have the for mula R -OR wherein R is selected from the group consisting of C to C secondary and tertiary alkyl radicals. R may also be a secondary cycloalkyl or tertiary cycloalkyl ligand having 3 to 7 carbons. R is preferably a C to C secondary or tertiary alkyl radical and most preferably a C to C tertiary alkyl radical.

R may be either a primary C to C alkyl radical or a secondary or tertiary C to C alkyl radical. C to C secondary or tertiary cycloalkyls may also be utilized; i.e., alkylcyclopropyl through alkylcycloheptyl ligands.

The promoter is used in conjunction with a Lewis acid. In brief, a Lewis acid is any molecule, radical or ion in which the normal electron grouping about a given atom is incomplete so that the atom may accept an electron pair or pairs. The promoter comprises a minor proportion of the catalyst and the Lewis acid comprises the major proportion of the catalyst excluding the support.

Such a catalyst is contacted at reaction conditions with a paraifinic feed stream, preferably a C through 0-; containing naphtha feed stream in which there is a substantial proportion of normal paraflinic hydrocarbons. The normal paraflinic hydrocarbons are isomerized and are converted to the desired state in which they possess higher octane.

Contacting of catalyst, promoter and feed stream is for extended periods of up to about 24 hours; temperatures are elevated and may range broadly from 30 to 300 F. Pressures may also be elevated and should range between 15 and p.s.i.g.

It is most preferred that the contacting take place within a solvent, the solvent is preferably a halo-aromatic solvent such as 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, l,2,4,5-tetrachlorobenzene, or pentachlorobenzene, and the corresponding bromo and fluoroaromatics. The highly substituted chloro and bromoaromatics including the hexahalo derivatives may also be used as solid supports by operating below the freezing point of the respective compounds. Following the contacting between the catalyst, promoter and feed stream, a product is recovered which is enriched in isomerized parafiins, at the same time, cracking of the feed stream is minimized and the ratio of isomerized products recovered to cracked products is improved. Comparing the promotional eifect of methyl-tamyl ether with t-amyl chloride (a well known and typical promoter) it is seen that the isomerization/cracking ratio obtained with the ether is about (35)/ 1 whereas With the alkyl halide it is about (0.51.5)/ l. The substantial increase in selectivity makes the ether the promoter of choice.

In more detail, the process of the instant invention relates to a method for isomerizing normal and isoparaflins and aliphatic naphthas, and in particular normal paraffins, isoparaflins and naphthas of C to C chain length. Typical isomerization reactions which would take place according to the process of the instant invention include the conversion of normal pentane to isopentane, normal butane to isobutane, normal hexane and a C naphtha to the equilibrium distribution of hexanes containing large amounts of 2,2-dimethylbutane and 2,3-dimethylbutane, and n-heptane and C naphthas to the highly branched isomers 2,2,3 trimethylbutane, 2,2- dimethylpentane, 3,3 dimethylpentane, 2,3 dimethylpentane and 2,4 dimethylpentane. The catalyst will also catalyze the isomerization of methylcyclopentane to cyclohexane which is valuable as a chemical intermediate, and the general isomerization of alkyl cycloalkanes to the equilibrium distribution of isomers.

Typical feed streams which would include normal parafiins in the C to C range are naphthas both virgin and cracked boiling between 10 and 210 F. The butane stream obtained at the tail end of the butane-olefin alkylation process and the paraffins remaining after extracting light olefins from cat cracked streams are also typical feeds for the process.

The above-mentioned feed streams are contacted, preferably in the liquid phase, with the combination of catalyst and promoter of the instant invention. Typical Lewis acids which may be effectively used for isomerization include aluminum chloride, boron trifluoride, antimony pentafluoride and aluminum bromide.

The other element of the catalyst or promoter, has the general configuration R OR R may be a C to C7 primary or C to C secondary or C to C tertiary alkyl group, and is preferably a methyl or ethyl group. Typical ligands which may be used for R include the following: methyl, ethyl, n-propyl and sec-propyl, isobutyl, sec-butyl and t-butyl, cyclopentyl etc. Cycloalkyls are included within the above categories. R differs from R in that R is restricted to secondary and tertiary alkyls or cycloalkyls. Most preferred ligands for R are the tertiary alkyls especially the t-butyl and t-amyl groups. The combination of catalyst and promoter is present in the proportion of about 90 to 99.9 mol. percent of catalyst to about 0.1 to 10 mol. percent of the promoter. Preferably about 95 to 99.5 mol. percent catalyst is utilized to about 0.5 to 5 mol. percent of the promoter.

The isomerization itself takes place preferably within a solvent although by using the haloaromatics below the melting point of the system a supported catalyst may be employed. A haloaromatic solvent is preferred and most preferably the solvent would be 1,2,3-trichlorobenzene, 1,2,4 trichlorobenzene, 1,2,4,5 tetrachlorobenzene, the corresponding fluorobenzenes and pentafluoro and hexafiuorobenzene, and 1,2,3-tribromobenzene and 1,2,4-tribromobenzene. Other halo aromatics include halogenated C through C aromatics including those which have condensed rings such as naphthalene. In general, liquid aromatics Whose basicity has been severely lowered by reason of the inclusion of a number of halogen atoms in their skeleton are acceptable solvents for the isomerization process.

Temperatures may vary widely; a broad range of about 30 to 300 F. may be used, preferably 70 to 200 F. Pressures may vary widely too but a range of 15 to 150 p.s.i.g. is acceptable. The preferred range for pressure would be between 15 p.s.i.g. and 100 p.s.i.g.

The contacting may take place in a batch or continuous operation. It is preferred to use a continuous operation in which flow rates of about 0.1 to about 5 v./v./hr. may be used. For a batch operation the following apparatus would be needed. A reactor made out of steel or monel, preferably containing inert walls; glass, porcelain or Teflon-lined although these are not required, and fitted with provisions for stirring, adding and withdrawing reagents is used for the isomerization. The products are separated from the catalyst by standard means such as by distillation. In a continuous operation, the apparatus would contain sections for the continuous introduction of feed to the reactor and for the continuous withdrawal of the catalyst-solvent-hydrocarbon system to a separator. Product would be collected at the separator and the catalyst and solvent would be recycled to the reactor. Provisions would be required for the continuous introduction of. small amounts of the catalyst and promoter to replace that which is consumed during the operation.

Aromatics and other basic materials that tend to be detrimental to the isomerization reaction may be substantially removed from the feed by conventional means,

such as with molecular sieves, or by acid treating, solvent extraction, mild hydrogenation or the like.

Although not intending to be bound by any specific theory as to operation, the following is offered to explain the favorable results of the instant invention, i.e., the minimization of cracking and maximization of isomerization.

Utilization of methyl-t-amyl ether as a promoter typical of this invention is believed to lead to the formation of Complex I which is in equilibrium with a tight ion pair, II. The t-amyl cation is believed to be relatively closely associated with the ether oxygen thus restricting its reaction possibilities. During the isomerization of a paraflin-like n-hexane, the t-amyl ion abstracts a hydride ion from n-hexane forming isopentane and a sec-hexyl ion. This is a necessary reaction for any isomerization catalyst.

The detrimental reaction which is impeded is one by which the t-amyl cation reacts with a bromine atom of the Rl Br molecule with which it is associated to form HBr and an olefin. If aluminum bromide is promoted with a conventional t-alkyl halide, the initial complex resembles III,

which is believed to ionize to yield an anion in which the charge is spread out over the bulk of the anion, (in contrast to the localized charge obtained with the ether). The cation is therefore less intimately bound to a given site of the anion and more readily reacts to form HBr and an olefin. Evidence that this model is valid may be obtained by measuring the pressure generated upon the addition of these promoters to the AlBr -1,2,4 Cl C H system. From the above it is apparent that in order to initiate the reaction at least one secondary or tertiary alkyl grouping must be present in the ether, i.e. as in methyl-tamyl ether.

SPECIFIC EMBODIMENTS EXAMPLE 1 In this example comparisons were made between t-amyl' chloride, t-amylalcohol and t-amylmethyl ether to determine their eifect on the isomerization of normal hexane. A solution of 0.25 ml. n-hexane and 0.5 ml. 1,2,4-trichlorobenzene was contacted with each of the three catalystpromoter systems under identical condtions. Temperature for all runs was 77 F., pressures were ambient and contacting times were 15 minutes. The homogeneous solution was allowed to stand for this time and products were recovered by vacuum distillation at room temperature.

TAB LE I Reaetant n-Hexane t-Amylt-Amylt-Arnyl chloride, alcohol, methyl Promoter, M e .02 M .02 M ether, .02 M

AlBra, M 0.5 0. 5 0. 5 onv., percent M5. 3. 8 5. 3 Isom/cracking b 1. 5/1 1. 6/1 4. 6/1

b 11 These are the promoter and AlBr; concentrations in 1,2,4-trichloroenzenes.

b The low isom/cracking ratio is characteristic of t-Amylchlorlde promotion, apparently independent of conversion. Other data at 8 and 48% coznvegsilop with .05 M AlBra and .04 M t-Amylohloride show 110 ratios of 1. an

The percent conversion was determined by a chromatographic analysis of the recovered products and the ratio of isomerization to cracking was determined by dividing the weight percent of C isomers by the combined Weight percent of all lighter and heavier components. A terse study of the table indicates that when making use of t-amylmethyl ether a ratio of isomerization to cracking which is three times as high was achieved. This indicates clearly a superior suppression of the cracking reaction.

EXAMPLE 2 In Table H the behavior of t-amyl chloride and methylt-amyl ether are compared over another catalyst at 149 F. Again 0.25 ml. of n-hexane was contacted with 0.5 ml. of 1,2,4-trichlorobenzene containing 0.5 M AlBr The promoter concentrations and reaction times were varied to permit an evaluation of the isomerization/cracking ratio as a function of reaction rate and conversion.

TAB LE II Selectivity Rate Relationships for n-Hexane Isomerizatlon in 0.5 M

AlBr31,2,4-O1 C0H 149 F.

Time, K, Isom./ Conver- Promoter M min. hr. crack. sion t-CtHnCl 0.02 15 0. 43 0.55 10. 1 t-CsHuCl 0. 002 15 0. 03 0.59 0. 9 t-CsHnOCHg- 0. 001 120 0. 02 4. 85 4. 0 t-CsHuOCHa 0. 005 60 0. 03 3. 23 3.0 t-CsHnOCHa 0. 01 15 0.06 3. 6 1. 6 t-CsHuOCHs 0.02 15 0. l3 3. 9 3.3

2 Apparent first order rate constant for hexane conversion to all produe s.

EXAMPLE 3 In this example the same conditions and reactants as in Example 1 are utilized except that methyl-t-butyl ether is substituted for t-amyl methyl ether, substantially identical results are observed.

Methyl-t-amyl other is a readily available compound that can be made by condensing Z-methyl-l-butene or 2- methyl-Z-butene with methanol in the presence of a small amount of sulfuric acid.

What is claimed is:

1. A process for isomcrizing paraflinic hydrocarbons into more highly branched chain parafiinic hydrocarbons which comprises contacting said hydrocarbons in the liquid phase, at reaction conditions with a Lewis acid catalyst and a promoter, said promoter being an ether having the formula R OR wherein R is selected from the group consisting of secondary, tertiary alkyl radicals and secondary, tertiary cycloalkyl radicals and R is selected from the group consisting of primary, secondary and tertiary alkyl radicals and secondary and tertiary cycloalkyls and wherein the amounts of said catalyst and said promoter present are in the proportion ranging from about -999 mole percent of catalyst to about 0.1-10 mole percent of the promoter.

2. The process of claim 1 wherein said parafiinic hydrocarbons are in a naphtha feed stream.

3. The process of claim 1 wherein said catalyst and said promoter are dissolved in a halogenated aromatic solvent.

4. The process of claim 1 wherein said parafiinic hydrocarbons are 0., to C7 paraflins.

5. The process of claim 1 wherein said catalyst is selected from the group consisting of aluminum chloride and aluminum bromide.

6. The process of claim 1 wherein the solvent is a trichlorobenzene.

7. A process for isomerizing a C through C paraffinic feed stream into more highly branched paraffins which comprises contacting said feed stream, in the liquid phase, at reaction conditions, with a major portion of a Lewis acid catalyst and a minor portion of a promoter, said promoter having the general configuration R OR wherein R is selected from the group consisting of C to C secondary, C to C tertiary and C to C cyclicalkyl radicals and R is selected from the group consisting of C to C primary, C to C secondary, C to C tertiary and cyclicalkyl radicals containing C through 0, rings, wherein said major portion of catalyst ranges from about 99.5 mole percent and the amount of said promoter ranges from about 0.5-5 mole percent and recovering an isomerized product.

8. The process of claim 7 wherein said contacting takes place within an organic solvent.

9. The process of claim 8 wherein said catalyst is selected from the group consisting of aluminum chloride and aluminum bromide.

10. The process of claim 8 wherein said solvent is a trichloro aromatic solvent.

11. The process of claim 8 wherein said ether is methylt-amyl ether.

12. The process of claim 8 wherein said contacting takes place at a temperature of 30 to 300 F.

References Cited UNITED STATES PATENTS 2,468,746 5/ 1949 Greensfelder et a1. 260-683.76 2,956,097 10/ 1960 Cull et a1. 260683.76 2,389,250 11/1945 Francis et al. 260683.75 2,393,569 1/ 1946 Ross et a1 260-683.75 2,406,633 8/1946 Pines et a1. 260683.76 3,190,940 6/ 1965 Walker et al 260683.75

DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner 

